Although iPhoto 6 is a simple program, it has fairly significant system requirements thanks to the difficulty of working with large digital images.
To run iPhoto, you need:
A Macintosh with a PowerPC G4, PowerPC G5, or Intel Core processor with 256 MB of RAM (though 512 MB of RAM is better). Realistically, the more CPU power and RAM you can throw at iPhoto, the better its performance. You'll also find a large monitor extremely helpful.
Mac OS X. Specifically, Mac OS X 10.3.9 or 10.4.3, but Apple recommends Mac OS X 10.4.4 and QuickTime 7.0.4 (which is included with iLife '06).
An optical drive that can read DVD discs, since iLife '06 comes on DVD. Burning DVDs directly from iDVD requires a drive that can write to DVD as well, such as an Apple SuperDrive or a third-party DVD burner.
A source of digital images, which could be an iPhoto-compatible digital camera, scanned images, Photo CDs, or a service that provides digital images along with traditional film developing. Apple maintains a list of cameras and card readers that are supposedly compatible with iPhoto at www.apple.com/macosx/upgrade/cameras.html. Take that list with a grain of salt; some devices on it may not work entirely, and some devices missing from the list work fine with iPhoto.
To be able to use iDVD for creating and burning slideshows to DVD, you need at least a 733 MHz PowerPC G4-based Mac.
iPhoto can import photos in RAW format, which is an uncompressed image file format used by some high-end cameras. However, there are multiple flavors of RAW, and iPhoto does not support all of them.